Conventional firearms are configured to chamber and fire a specific cartridge. If the user wishes to fire a different cartridge, the user must obtain a different firearm that is chambered to handle the cartridge. Unfortunately, it is rarely practical to obtain large numbers of firearms of varying calibers. Instead, most people carefully evaluate what the firearm will be used for and select the cartridge that best meets the majority of the user's needs. For example, someone who uses the firearm primarily for African game is likely to choose a magnum caliber, while someone who uses the firearm primarily for varmint hunting is more likely to choose a lighter, faster, standard caliber.
It should be noted that the term “caliber” can have a variety of different meanings. For example, the caliber may refer to: (1) the approximate size of the bullets fired through a firearm (e.g., .17 caliber bullets; the actual diameter of .17 caliber bullets is 0.177 inches), (2) the approximate size of the inside diameter of the barrel of the firearm (e.g., a .30 caliber rifle; the actual inside diameter of the barrel of a .30 caliber rifle is 0.308 inches), or (3) the specific cartridge that the firearm is configured to chamber (e.g., .300 Winchester Magnum). For example, a rifle that is configured to fire 30-06 cartridges may be appropriately referred to as simply a .30 caliber rifle because that is the approximate size in inches of the bullets (the actual size of the bullets is 0.308 inches) and the inside diameter of the barrel. However the same rifle may also be appropriately referred to as being a 30-06 caliber rifle since that is the specific cartridge that the rifle is chambered for.
Some conventional firearms are capable of firing more than one caliber of cartridges. For example, most .357 magnums are also capable of firing .38 special cartridges. The primary difference between the two cartridges is that the .38 special is significantly shorter. Otherwise, the diameter of the bullets and the outside diameter of the rims of the two cartridges are the same. Most firearms that can fire multiple cartridges involve situations such as this where the cartridges are very similar or identical in size, particularly the outside diameter of the bullet and the rim of the cartridge case (e.g., a .22 long rifle caliber firearm can usually fire .22 shorts and .22 longs).
It would be desirable to provide a firearm that is capable of firing a much wider variety of cartridges. Such a firearm may eliminate or reduce the perceived need to buy multiple firearms depending on how the firearm is intended to be used.